Gramophone pick-up



Dec. 29, 1936. E. N. JOHNSON GRAMOPHONE PICK-UP Filed Oct. 8, 1935 M Mfi h w W Patented Dec. 29, 1936 UNITED STATES GRAMOPHONE PICK-UP Edward Noel Johnson, Johannesburg, Transvaal, Union of South Africa Application October 8, 1935, Serial No. 44,119 In Union of South Africa October 6, 1934 3 Claims.

The present invention relates to gramophone pick-ups and more generally to means for producing electrical oscillations from a mechanical sound record having an undulating sound track such as to oscillate a stylus which traverses it; of the kind in which the oscillating stylus carrier also carries a mirror by which a beam of light is reflected and oscillated correspondingly with the stylus and in turn actuates a photo-electric device by which there is produced an electric current corresponding to the stylus oscillations.

An object of the invention is to improve such known apparatus, particularly as regards fidelity of the reproduction and by enabling volume control to be eifected by variation in the intensity of the light.

According to the invention the reflected and oscillatory beam of light is split, as by a V shaped mirror, into fractions which relatively vary in magnitude, correspondingly with the direction and amplitude of displacement of the reflected beam. The fractions are delivered to separate photo-electric devices so as to energize the latter in push-pull manner. The electric currents produced by the photo-electric devices are amplified and combined by means of a push-pull amplifier.

Apparatus according to the invention for operating with a laterally out sound record is illustrated in the accompanying drawing, in which:

Figure I is a perspective View of the apparatus.

Figure II shows the path of the light beam.

2 indicates a pedestal upon which a tone arm 3 is pivotally mounted to enable the stylus 4 to 5 follow the sound track. 5 indicates the housing for the stylus carrier, comprising the base 6 fixed to the tone arm 3, two bearing plates 1, 8 and a clamping plate 9; the assembly being held together as by studs l0 fixed to the base 6 and passing through the three upper plates. The bearing plates 1, 8 provide the half-bearings for the spindle of the stylus carrier ll, l2.

The stylus carrier comprises a stylus socket I2 rigid with the spindle II. The stylus 4 is clamped in its socket l2 by clamping screw l3 which operates in an internally threaded end of the spindle II. The other end of the spindle H is extended to carry light-diverting means such as a mirror 14 which is rigidly attached to and vibrates with the stylus carrier.

The light beam is derived from the lamp I5 fixed to the tone arm 3 and fitted with a lens It for producing an approximate image of the filament I! on the photo-electric cells. The filament I1 is arranged parallel to the axis IS with the object of providing a reflected light beam !9, shown in Figure II, which is narrow in its direction of movement indicated by the double headed arrow A and long in the opposite cross sectional dimension. The reflected light beam is arranged to influence a pair of photo-electric cells 20, 2| arranged in push-pull relationship.

Numerals 22, 23 indicate a pair of mirrors angularly arranged to one another and meeting at the edge 24. They are shown as provided by 10 the polished surfaces of a metal bar rigidly fixed to the tone arm 3 to which the cells 25], 2| are also fixed. When the mirror I4 is at rest, the light beam I 9 is divided by the edge 24 into fractions 19a, I9b having a definite volume relation- 15 ship to one another,-conveniently equal to one another. Said split portions of the beams are reflected to the cathodes 25, 26 of the photoelectric cells. The latter are enclosed in casings 21 which exclude stray light, and which are apertured at 28 to permit free ingress of the split beams. The removable portion of one of these casings is omitted in the drawing, in order to show its cell 20.

The electrical outputs of the cells 20, 2| are amplified and combined by the push-pull amplifier 28 and transmitted to the loud speaker 21.

As the mirror l4 oscillates, the proportions of the split beams are altered. The amount of light received by their respective photo-electric 30 cells is similarly altered; and so the electrical output of the cells.

By splitting the light beam as described, applying the fractions to the two photo-electric cells in push-pull relationship and thereafter combining their outputs, the detrimental influence of the curvature of the cells characteristics is neutralized and eliminated before the loud speaker is reached. This results in improved fidelity and reproduction and moreover enables the sound voliune to be controlled by variation of the intensity of the light emitted from lamp l1, without accompanying distortion of the sound. 45

I claim:

1. The process of producing sound from a mechanical sound record, which consists in. traversing the sound track of said record, by a stylus and thereby oscillating the stylus, imp-art- 50 ing the oscillations of the stylus to a beam of light, splitting the oscillating light beam into fractions relatively varying in magnitude, separately delivering the beam fractions to two photoelectric devices arranged in push-pull re- 55 V lationship, and'combining the electrical outputs of said devices.

2. Apparatus for producing electrical oscillations from a stylus adapted to be oscillated by traversing the sound track of a mechanical sound record, comprising means, to produce a beam of I 1* p 9 2,006,208 Q1 1 arranged in push-pull relationship and so as to receive respectively the split portions, and means to combine the outputs of said devices.

3. Apparatus as claimed in claim 2, comprising a push-pull amplifier arranged for amplifying and combiningthe electrical outputs of the V photoelectric "devices.

EDWARD NOEL JOHNSON. 

